• Structural Engineering and Mechanics
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• 제65권1호
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• pp.81-89
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• 2018

Stone column installation is a convenient method for improvement of soft ground. In very soft clays, in order to increase the lateral confinement of the stone columns, encasing the columns with high stiffness and creep resistant geosynthetics has proved to be a successful solution. This paper presents the results of three dimensional finite element analyses for evaluating improvement in behaviour of ordinary stone columns (OSCs) installed in soft clay by geotextile encasement under monotonic and cyclic loading by a comprehensive parametric study. The parameters include length and stiffness of encasement, types of stone columns (floating and end bearing), frictional angle and elastic modulus of stone column's material and diameter of stone columns. The results indicate that increasing the stiffness of encasement clearly enhances cyclic behaviour of geotextile encased stone columns (GESCs) in terms of reduction in residual settlement. Performance of GESCs is less sensitive to internal friction angle and elasticity modulus of column's materials in comparison with OSCs. Also, encasing at the top portion of stone column up to triple the diameter of column is found to be adequate in improving its residual settlement and at all loading cycles, end bearing columns provide much higher resistance than floating columns.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.132-143
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• 2003

Viscoelastic components for vibration isolation or shock absorption in automobiles, machines and buildings are often subject to a high level of static deformation. From the dynamic design point of view, it is requisite to predict dynamic complex stiffness of viscoelastic components accurately and efficiently. To this end, a systematic procedure for complex modulus measurement of the viscoelastic material under large static deformation is often required in the industrial fields. In this paper, dynamic test conditions and procedures for the viscoelastic material under small oscillatory load superimposed on large static deformation are discussed. Various standard test methods are investigated in order to select an adequate test methodology. The influence of fixed boundary condition in the compression tests upon complex stiffness are investigated and an effective correction technique is proposed. Then the uniaxial tension and compression tests are performed and its results are compared with analysis results from conventional constitutive models.

• 한국지반공학회지:지반
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• 제4권4호
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• pp.29-38
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• 1988

약액주입도결토에 대한 연구의 주 목적중 하나는 약액주입으로 인한 토성변화를 연구하는 것이다. 특히 약액주입으로 인한 흙의 탄성계수나 전단계수와 강도특성의 변화는 우리의 관심을 끌어왔다. 본 연구에서는 입경에 따라 비표면적이 변화하므로 이에 의한 영향을 구명하고져 미고결기와 고 결토에 대한 일축압축 및 삼축압축시험을 실시하여 사질토의 장경이 물유리계약액고결토의 강도 및 강성에 미치는 영향에 대해 고찰하였다. 연구결과 시료토의 날경이 작을수록 고결토의 강도 및 강주이 증대되는 것이 발견되었으며, 모래의 비표면적과 약액겔강도와의 상관성을 구명함으로써 고결토의 담담추정의 가능성을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.382-387
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• 2004

Nanoindentation technique has been used to measure the mechanical properties of aluminium alloy foam cell walls. Al-Si-Cu-Mg alloy foams of different compositions and different cell morphologies were produced using powder metallurgical method. Cell morphology of the foam was controlled during production by varying foaming time and temperature. Mechanical properties such as hardness and Young's modulus were calculated using two different methods: a continuous stiffness measurement (CSM) and an unloading stiffness measurement (USM) method. Experimental results showed that hardness and Young's modulus of Al-5%(wt.)Si-4%Cu-4%Mg (544 alloy) precursor and foam walls are higher than those of Al-3%Si-2%Cu-2%Mg (322 alloy) precursor and foam walls. It was noticed that mechanical properties of cell wall are different from those of precursor materials.

• Steel and Composite Structures
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• 제41권6호
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• pp.887-898
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• 2021

This paper presents a simplified model to capture the nonlinear behavior of steel frames depending on the spread of plasticity method. New interaction formulae were derived to evaluate the plastic strength for I-shaped steel sections under uniaxial bending moment and axial compression load. Also, new empirical formulae were derived to evaluate the tangent stiffness modulus of steel I-shaped cross-sections considering the effect of the residual stresses suggested by the specifications in European Convention for Construction Steelworks (ECCS). The secant stiffness which depends on the tangent modulus is used to evaluate the internal forces. Based on stiffness matrix method, a finite element analysis program was developed for the nonlinear analysis of space steel frames using the derived formulae. Comparison between the proposed model results with those given by the fiber model shows very good agreement. Numerical examples were introduced to verify, check the accuracy, and evaluate the efficiency of the proposed model. The analysis results show that the new proposed model is accurate and able to minimize the solution time.

• 한국자동차공학회논문집
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• 제7권9호
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• pp.89-96
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• 1999

This paper presents the optimization design technique on the joint stiffness and section characteristic factors of chassis frame, by using beam and spring elements in a given design package. Two correction methods are used for the optimization design of chassis frame. First is the equivalent inertia of moment method in relation to the section characteristic factors of joint zones, which are thickness , width and height of frame channel section. Second is the rotational spring element with joint stiffness of joint zones. The CAE example shows that the relationship of section characteristic factors and joint stiffness can effectively be used in designing chassis frame. In this point, if static and dynamic targets are given, the joint-zone and section characteristic factors of chassis frame intended may be designed and defined by using beam and rotational spring elements.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.129-132
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• 2006

It is generally reported that most of RC beams strengthened with simply bonded FRP composite is failed by FRP debonding. Also, the flexural performance of RC member strengthened with FRP composite can be calculated using the effective strain of FRP. The effective strain as a result of the debonding failure depends on many variables, such as FRP stiffness including the thickness($t_f$) and modulus of elasticity($E_f$), the amount of FRP but the FRP stiffness is reportedly the most influential. The purpose of this paper, therefore, is to examine effects of FRP stiffness on the flexural strengthening of RC beams. 4 different stiffness of CFRP composite including CFRP sheet and laminae were selected. From the tests, it was found that the flexural performance of RC beams strengthened with CFRP composite can be calculated based on the effective strain of the CFRP composite and the effective strain is inversely proportional to the CFRP stiffness.

• 대한토목학회논문집
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• 제28권4A호
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• pp.475-485
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• 2008

이 논문은 국내 탄성받침의 성능과 신뢰성 향상을 위한 일환으로, 탄성받침의 설계/제작/품질평가 기준인 KS F 4420의 강성 관련 개선방향을 제안하였다. 이를 위하여 KS F 4420의 압축탄성계수, 강성측정방법, 성능평가방법을 Eurocode, 일본 도로교지승편람, ISO 기준과 비교 분석하였으며, KS F 4420의 강성 제안식과 실측치와의 차이를 알아보기 위하여 국내 일반적인 탄성받침을 대상으로 수직강성과 전단강성 측정 실험을 실시하였다. 실측된 수직강성은 강성정의 방법에 따라 20%정도 차이를 나타냈으며, 전단강성은 13%정도 차이를 나타냈다. 또한 실측된 강성은 KS F 4420의 제안식과의 편차도 큰 것으로 나타났다. 교량받침이 요구되는 수직강성을 가지지 못하는 경우 교량 상부 구조물의 부등침하 및 응력집중 현상을 야기할 수 있다. 따라서 국내 받침이 설계에서 요구되는 성능을 갖기 위해서는 다양한 형상, 형상계수를 갖는 받침의 성능평가를 통하여 국내 실정에 맞는 압축탄성계수식과 성능평가기준의 마련이 필요하다고 판단된다.

• Advances in nano research
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• 제9권2호
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• pp.83-90
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• 2020

This research investigates the effect of single walled carbon nanotubes (SWCNTs) dimensions in terms of diameter on the mechanical properties (longitudinal and transverse Young's modulus) of the simulated nanocomposites by molecular dynamics (MDs) method. MDs utilized to create nanocomposite models consisting of five case studies of SWCNTs with different chiralities (5, 0), (10, 0), (15, 0), (20, 0) and (25, 0) as the reinforcement and using polymethyl methacrylate (PMMA) as the common matrix. The results show that with increasing of SWCNTs diameter, the mechanical and physical properties increase. It is important that with the increasing of SWCNTs diameter, density, longitudinal and transverse Young's modulus, shear modulus, poisson's ratio, and bulk modulus of simulated nanocomposite from (5, 0) to (25, 0) approximately becomes 1.54, 3, 2, 1.43, 1.11 and 1.75 times more than (5, 0), respectively. Then to validate the results, the stiffness matrix is obtained by Materials studio software.

• 한국농공학회논문집
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• 제52권2호
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• pp.19-25
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• 2010

This study was conducted to determine the resilient modulus (Mr) and the unconfined compressive strength (UCS) of two recycled roadway materials such as recycled pavement material (RPM) and road surface gravel (RSG) with or without cement kiln dust (CKD). The recycled materials were blended with two CKD contents (5, 10 %) and 28 day curing time. Mr and UCS tests were also conducted after 10cycles of freezing and thawing to asses the impact of freeze-thaw cycling. Mr was determined conducting by the laboratory test method described by NCHRP 1-28A. Stabilized RPM and RSG had a modulus and a strength higher than unstabilized RPM and RSG. Mr and UCS of RPM and RSG mixed with CKD increased with increasing CKD content. The results indicated that the addition of CKD could be improved the strength and the stiffness of RPM and RSG. Therefore, RPM, RSG and CKD could be used as an effective materials in the reconstruction of roads.